1. Field of the Invention
The present invention relates in general to adjustable wrenches commonly used in tightening and loosening different-sized bolts and nuts and, more particularly, to a structural improvement in such adjustable wrenches for facilitating use of the wrenches for tightening or loosening the bolts and nuts of different sizes by changeable fitting of size-adjusting blocks with eccentric fitting means in a wrench head.
2. Description of the Prior Art
With reference to FIG. 1, there is shown a typical wrench used in tightening or loosening a bolt and nut, which wrench is provided with opposed heads 52 and 52' integrated with both ends of a wrench handle 55 into the wrench. Each of the heads 52 and 52' has a pair of fixed jaws 50 or 50', thus to form a grip opening 51 or 51' between the jaws 50 or 50'. However, as the grip openings 51 and 51' of the above wrench have fixed grip sizes, the wrench is inevitably limited in its use. Therefore, the above wrench has a problem that a variety of wrenches of different sizes should be prepared for selective use of wrenches in tightening or loosening a corresponding variety of bolts and nuts of different sizes. As a variety of wrenches of different sizes should be prepared as described above, the wrenches may be lost and increase the cost.
In order to counter the above problems of the wrench having a fixed grip size, there have been proposed adjustable socket wrenches as disclosed in Korean U.M. Publication Nos. 85-1175 and 86-3147. FIG. 2 shows an example of the typical adjustable socket wrenches. As shown in the drawing, the typical adjustable socket wrench includes a head 60 coupled to an end of a handle 65 by means of a shaft 61. The head 60 has an adjustable grip opening 62, which opening 62 is formed by a fixed jaw 60a and a movable jaw 60b. The movable jaw 60b is movable with respect to the fixed jaw 60a by a turning motion of an adjusting worm 64 so that the size of the grip opening 62 is adjusted and fitted to the head size of a bolt or nut to be tightened or loosened.
However, the above adjustable socket wrench has a problem that as the size of the grip opening 62 is adjusted by the turning motion of the adjusting worm 64, the adjusting worm 64 may be abraded or broken due to pressure repeatedly applied thereto whenever tightening or loosening bolts and nuts and this reduces durability of the wrench. Whenever tightening or loosening bolts and nuts of different sizes, the adjusting worm 64 should be turned in order to fit the size of the adjustable grip opening 62 to the size of bolt or nut. Therefore, the above wrench still has an inferior wrench work efficiency.
Additionally, the construction of above adjustable socket wrench is so complicated that the wrench is produced at high cost. Another problem of the above adjustable socket wrench resides in that the size of the grip opening 62 adjusted by moving the movable jaw 60b relative to the fixed jaw 60a is limited to a predetermined range so that the above adjustable socket wrench still has the problem of size limitation.